It is often desired to connect components using welding to form a hermetically sealed connection. Medical devices, including encapsulated IMDs, frequently comprise a case structure (or similar component) and one or more fixtures, such as fillports for liquid electrolyte, electrical feedthroughs (e.g., multipolar and single-pin feedthroughs), ferrules, sensors, needles, nozzles, electrical connectors, and similar components, that establish electrical communication through the case with a hermetic seal.
Implantable medical devices (IMDs) include pacemakers, cardioverters, defibrillators, and other devices for therapeutic stimulation of the heart, as well as other devices such as implantable devices for administering drugs. Such devices can include a flat electrolytic capacitor (FEC), a wet valve metal-slug capacitor (e.g., a high energy wet tantalum capacitor), a primary or secondary battery, a drug pump, an infusion pump and the like. An example is the IMD set forth in U.S. Pat. No. 6,118,652 entitled “Implantable Medical Device Having Flat Electrolytic Capacitor With Laser Welded Cover.”
In one application, one or more FEC stores energy required for defibrillation and other procedures performed by the medical device. An FEC typically includes an electrode assembly having an anode structure, a cathode, a separator (or spacer), an electrolyte (which can function as the cathode), and a case for enclosing the capacitor and containing the electrolyte. The capacitor stores energy in an electric field generated by opposing electrical charges on either side of an oxide layer formed on the anode. The energy stored is proportional to the surface area of the anode. The oxide layer is generally formed during electrolysis, where electrical current is passed through the anode.
Tabs or terminals can extend outside the case for electrically connecting the capacitor to external objects (e.g., to electrode coils disposed in electrical communication with myocardial tissue of a subject). Feedthroughs can be used to form electrical or other connections that extend through the FEC case.
A fillport is typically connected to the capacitor case during fabrication. The fillport permits a fluid, namely the electrolyte, to be introduced into the case at an appropriate stage during fabrication. Once the capacitor has been filled with electrolyte, the fillport can be cut or trimmed close to the case and then capped as part of a process of sealing the electrolyte within the capacitor. The capacitor utilizes hermetic seals for preventing fluids from the capacitor from leaking, which is impermissible when the medical device is implanted in a host body. In addition, hermetic seals help assure proper function of the capacitor and the medical device by limiting contamination and preventing necessary fluids from draining.
Known manufacturing processes for attaching two components with a hermetic seal present a number of problems and limitations. Typically when manufacturing medical devices, according to those known methods, fixtures such as fillports are placed at an opening on the case, protruding outward from the case. A flange on the fillport rests along an outer surface of the case and a sealing or connection portion of the fillport is situated within the opening. The fillport is typically temporarily held in place at the opening by gravity or a vacuum. The fillport and case are then welded together by creating a weld, often a laser weld, between the flange of the fillport and the exterior surface of the case. This weld resembles a lap joint. Welds formed between the flange on the fillport and the exterior of the case often exhibit poor weld penetration. The weld must penetrate three oxide layers, which are located on the flange of the fixture (i.e., top and bottom surfaces of the flange) and the exterior surface of the case. Welding though oxide layers is difficult.
In addition, these welds leave small gaps or crevices between the fillport and the case between the weld (on the exterior surface of the case) and an interior surface of the case. Stress points are formed at such gaps or crevices, which can result in poor weld and seal integrity. This can lead to a broken seal and also a broken connection, which are collectively referred to as weld failures. Furthermore, when the case contains a fluid, for example when the case is part of a FEC containing an electrolyte, fluid can collect within gaps and crevices between the fillport and the case (between the weld and the interior surface of the case), which causes processing issues, crevice corrosion, and exacerbates undesirable stresses at such locations.
Moreover, the fixture can become misaligned during manufacturing, leading to an improper connection and/or seal. With known manufacturing processes it is difficult to clamp or otherwise secure fixtures to a case component while welding. This makes it difficult to deal with misalignment problems.
Further, manufacturing processes are generally limited to manipulating a laser beam or other welding means from a position relative to the exterior surface of the case. In some instances the laser beam inadvertently impinges upon a portion of a component to be welded (e.g., an elongated fillport tube protruding toward the laser source), thus reducing yield and increasing scrap and costs related thereto.
Thus a more reliable sealed connection between two components, and a method of creating such a connection, is needed.